object Program extends App {
  
  // immutable, equivalent to 'final'
  val x = 1
  println("val x="+x)
  
  // mutable
  var y = 2
  println("var y="+y)
  
  //compiler error: reassignment to val
  //x = 3
  //println("val x="+x)
  
  y = 4
  println("var y="+y)
}